An active energy ray-curable resin composition is used in various fields such as a hard coating agent for various plastic substrates of home electric appliances, cellular phones, and the like, an over-coating agent for paper and the like, a binder for printing inks, a solder resist, and the like from the viewpoint of the characteristics of little heat history to coating substrates and excellent hardness and scratch properties of coating films.
In the application to a binder for printing inks among these applications, an active energy ray-curable ink for offset printing attracts attention in view of a low environmental load, and a diallyl phthalate resin is currently widely used as a binder resin in view of excellent printability, little elution of low-molecular-weight components, and solubility in UV monomers.
However, the toxicity of diallyl phthalate used as a raw material of the diallyl phthalate resin has recently been pointed out, and thus there is increasing demand for a printing ink using an active energy ray-curable resin instead of the diallyl phthalate resin.
A urethane acrylate resin is known as an active energy ray-curable resin other than the diallyl phthalate resin, and the urethane acrylate resin is likely to be applied to printing inks in view of its excellent physical property balance and is produced by, for example, reacting a polyfunctional isocyanate compound with 2-hydroxyethyl acrylate at a ratio such that isocyanate groups are excessive, and then reacting the residual isocyanate groups of the resultant reaction product with acid diol and polyol (refer to Patent Literature 1).
The urethane acrylate resin produced by the production method does not contain 2-hydroxyethyl acrylate having high skin irritation and remaining in the resin and thus is excellent in safety and sanitation in handling printing inks. However, curability is inevitably decreased due to decrease in the concentration of functional groups in urethane acrylate, and offset printing has poor printability due to a high content of acid groups.
On the other hand, a resin known as a urethane acrylate resin having no acid group, for example, as a urethane acrylate resin for coating, is produced by reacting a polyfunctional isocyanate compound with a high-molecular-weight polyol such as polyester polyol or polyether polyol and then reacting the reaction product with 2-hydroxyethyl acrylate (refer to Patent Literature 2).
However, the urethane acrylate resin has a relatively high molecular weight for the purpose of improving resilience in coating application and has a small amount of modification of 2-hydroxyethyl acrylate from the viewpoint of imparting flexibility. Therefore, when used for printing ink application, satisfactory curability cannot be achieved, and also offset printing has poor printability.